Plant breeding and genetically modified food

The Slovene word for plant breeding žlahtnjenje is really difficult to pronounce. I have already been asked by journalists if it could be replaced with a better-sounding word, which is not surprising since most people even spell it wrong and leave out at least one “j”. To make it even more confusing it is often translated incorrectly and all the English-Slovene dictionaries offer misleading equivalents. The terminology is very confusing so it is not surprising that there is an even greater confusion when it comes to understanding the topic.

I sometimes give lectures to high school students. The first thing I tell them is that we would not be sitting in the classroom having a nice chat if not for the generations of plant breeders in the past century whose work dramatically increased the number of crops of all the leading cultivars. We would not be talking, because we would probably be out digging potatoes. Students simply do not realise that not too long ago, just before World War II, sixty per cent of the population were farmers, and yet many people still went to bed hungry. In addition, many youngsters do not know where this abundance and diversity of food suddenly came from, nor even that it comes from increasingly smaller farmed areas. If anything, they know that today’s fields are ploughed with tractors and not horses, and that mineral fertilisers are used instead of manure. They also know about the use of synthetic pesticides and herbicides, soil irrigation and drainage. But very rarely do I hear anyone say that we are sitting here because of the modern varieties of cultivars. And yet according to science, the massive increase in crop yields, producing five times as much from the same farmland than a hundred years ago, is largely due to the breeding of new plant varieties.

Plant breeding obviously developed before the 20^th century. People have been selecting plants for millennia, but it was not until great discoveries, such as that of America, that the most successful species spread across the world for the first time. It is actually quite unbelievable how much people have achieved without knowing anything about inheritance. It took several decades to come up with scientific proof that the unimpressive teosinte plant is really the sole ancestor of today’s mighty corn. Similarly, it is hard to believe that such different vegetables as cabbage, cauliflower, kale, kohlrabi, Brussels sprout and broccoli are actually all cultivars of the same species named Brassica oleracea. The history of plant breeding reveals the start for every presently autonomous variant. Most of the above-mentioned varieties exist thanks to the Roman Empire.

As in all other fields, the progress in plant breeding was gradual. Mass hybridisation and plant selection, intraspecific as well as interspecific, was performed as early as the 18^th and 19^th centuries with the production of the first modern varieties. Even today, many pear and vine varieties from that era are still being grown. Although Gregor Mendel’s discoveries in 1900 are considered the scientific basis of this field, many other less-known discoveries are equally important.

Progress was much faster after discovering how to cultivate self-pollinating plants, such as wheat or peas, cross-pollinating plants like rye and onion, and vegetatively multiplied plants, which include all fruit types. But it was not until the discovery of hybrid species that the seed trade showed real entrepreneurial spirit. It all started with corn and continued with more and more species. In fact, a hybrid has three important advantages: one to the seed trader’s benefit and the other two to the farmer’s. Firstly, the hybrid guarantees the farmer a more uniform crop, even with cross-pollinating plants. The difference is immediately noticeable if a non-hybrid cabbage cultivar is sown next to a hybrid cultivar. Secondly, the hybrid enables the farmer to get larger yields because it exhibits hybrid vigour. But the seed trader is just as satisfied with the outcome: the farmer needs to buy seeds every year because planting a new generation would not pay off due to diversity related issues. Interestingly, hybrid vigour and related theories have existed for almost a hundred years, and yet the molecular background has not been fully explained until recently with new genetic discoveries. It is an educational story indicating how practice often overtakes theory. Today, hybrids dominate in most important cultivated species, regardless of the complicated nature of plant breeding methods and annual seed production. Recent research shows that species like wheat, where hybrids are not yet as established, show slower progress than species where hybrids dominate. This is largely due to the interests of the seed companies, investing more into species that ensure annual sales.

Each plant breeding process starts with selecting and usually crossbreeding numerous varieties. For this purpose, breeders need as much genetic diversity as possible, which can be found in new and old varieties, in local populations and even in other, mostly wild-growing related species. Preserving biodiversity that is crucial for farming has been in the foreground for nearly ninety years. During this time, numerous gene banks storing millions of samples have been established, and one of them is also found in Slovenia. These samples are used to provide sources of genetic diversity, which go through long selection procedures before they are included in new varieties. More information on gene banks is available here.

Various vegetables such as cabbage, cauliflower, kale, kohlrabi, Brussels sprout and broccoli are all cultivars of the same species, Brassica oleracea. (Photo via gman-bioblog.blogspot.com)

How exactly are new varieties created and why is genetic modification necessary?

The basic methods of plant breeding are hybridisation, self-pollination, reverse breeding, cloning and mutation induction. These processes rarely take less than ten years, and it is common in the meantime for the plant breeder to exclude thousands or even tens of thousands of crosses. In addition to the basic methods, a range of tissue culture techniques has been developed to produce pure lines from gametes and achieve homozygosis in only one year. All European rapeseed varieties are produced using this method. Intraspecific hybridisation is achieved with in vitro embryo rescue, which enables the production of numerous new citrus fruits that can be found in supermarkets. Apart from hybridisation, it is also possible to fuse two nuclei of different species using protoplast fusion, which fuses somatic cells with removed cell walls. As previously mentioned, using hybrids, more precisely crosses of two pure lines, has proven to be most efficient but their production is very complicated. For this purpose, male sterile lines are used to avoid manual removal of stamens. For example, protoplast fusion of chicory and sunflower enabled chicory to produce hybrid varieties. Selected crosses go through an increasingly thorough selection process because laboratory techniques including genetic markers, sequencing, proteomics and so on enable the inspection of previously hidden cell processes. The selection process is facilitated by phytopathological tests used to select resistant varieties, and complex laboratory analyses which show the presence of different metabolites. A representative of a seed trade company once said: “Jožef Jerič explained to us that this corn was produced using genetic technology, which makes it possible to select genes that enable the plant to preserve moisture even in extreme drought conditions and not dry out.” What he meant was that plant breeding of new varieties was performed using genetic markers, which represent a breakthrough in this field.

Then why is the genetic modification method even needed? The answer is multifaceted. Firstly, it is needed to fulfil certain goals that cannot be achieved by using ordinary methods. For example, if no rice sample contains vitamin A, using hybridisation will not help achieve the goal. Secondly, because it means they can be more easily achieved: it is simple to breed courgettes resistant to several viruses using genetic engineering, while it is almost impossible to do the same through hybridisation. Thirdly and most importantly, genetic modification is used to produce species with completely new characteristics (e.g. vegetable oil with omega-3 fats). Lastly, it could be related to the intention of using plant species as cheap producers of industrial and pharmaceutical substances. You can read more about rice for health purposes here, and the potato for industrial production (Amflora) here.

Legal regulations regarding plant breeding and release on the market or in production are quite different from those concerning plant breeding of ordinary varieties. There are many laws and rules that regulate this field. For more information on this topic click here. The essential part of these processes involves gradual use of the following phases: laboratory tests, tests in a secure environment, smaller field tests and production. The applicant must provide detailed information, which is carefully examined by the national and the European science committees, frequently followed by a request for additional information. Regulatory bodies then provide a publicly accessible opinion on each application, and one of them can be accessed here. Simply skimming through the text is enough to realise how thoroughly the new products are tested.

The media dedicates a lot of attention to the production of genetically modified plants. The most frequent questions and statements have already been addressed on this site, and there is also an article on Meta’s List about successful examples of genetic modification.

Author: Borut Bohanec, lectures on plant breeding and plant biotechnology, as well as being Head of Chair and Deputy Dean at the Department of Agronomy at the Biotechnical Faculty, University of Ljubljana. He is a lightning conductor for politicians, self-proclaimed environmentalists and ringleaders of organic agriculture. Follow him on twitter @BorutBohanec.